1. Field of the Invention
This invention relates to a system for charging battery cells used in portable electronic equipment and, in particular, to a charging system including a charger having a simplified structure for a battery pack including a processor.
2. Description of the Related Art
Lithium-ion batteries and nickel-hydride batteries, which have high energy densities, are often used in laptop personal computers (hereinafter referred to as laptop PCs), which are typical portable electronic equipment, because the laptop PCs require higher central processing unit (CPU) operating frequencies, longer operating times in mobile environments, and smaller sizes and lighter weights. To charge and discharge these batteries, recharge and discharge currents and voltages must be precisely controlled. Therefore, rather than conventional battery packs having only battery cells in a housing, battery systems called “smart batteries” are commonly used in which a microcomputer provided in the battery pack itself communicates with a laptop PC to exchange information while controlling charge and discharge.
Smart batteries are battery systems that are compliant with specifications called the Smart Battery System (SBS) specification proposed by Intel Corporation and Duracell Inc. in the United States. The first version, version 0.9, of the SBS specification was disclosed in 1995 and the latest version is Version 1.1. The SBS specification's main aim was to unify methods for controlling charge and discharge, measuring capacities, and communicating with laptop PCs, which had been being developed by laptop PC manufacturers on their own, to enable a battery pack itself to perform control of charge and discharge suitable to the chemical composition of the battery pack, thereby relieving the laptop PC designers of recharge/discharge control design work. Battery packs compliant with the SBS specification are referred to herein intelligent batteries.
An intelligent battery includes battery cells, which are the main unit to be charged and discharged, and electric circuitry including a CPU, a current measurement circuit, a voltage measurement circuit, and sensors contained on a substrate. In addition, the intelligent battery communicates with an embedded controller provided in a laptop PC through a data line. The intelligent battery can cooperate with the laptop PC to change a power consumption mode of the laptop PC in accordance with the remaining capacity of the battery or to shut off the laptop PC after displaying a warning on a display if remaining capacity becomes small or some abnormality occurs on the battery.
Two types of intelligent battery chargers, Level 2 and Level 3, are defined in the section “4.2 Smart Battery Charger Types” of the SBS specification “Smart Battery Charger Specification” Revision 1.1, released Dec. 11, 1998. In the case of the Level 2 battery charger, the intelligent battery is a master device and the battery charger is a slave device following the directions of the intelligent battery. The intelligent battery sends information about a current and voltage required for charging to the battery charger through a data line. The battery charger outputs a current and voltage based on the information. The Level 3 battery charger has a charger master operation mode in which the battery charger is the master device and the intelligent battery is the slave device following the battery charger. The Level 3 battery charger also has the battery master mode of the Level 2 battery charger. In the charger master mode, the battery charger sends an inquiry about a current and voltage required for charging to the intelligent battery and outputs a current and voltage according to a replay to it.
While a laptop PC equipped with a battery pack is being supplied with power from an alternating current (AC) power source, the battery pack is concurrently charged through a battery charger contained in the laptop PC. The laptop PC can then be used in a mobile environment. A user using a laptop PC in a mobile environment for a long time must charge spare battery packs beforehand. This requires many external battery chargers and places an extra cost burden on the user.
FIG. 7 shows a basic configuration of a conventional charging system. FIG. 7(A) shows a conventional battery pack 10′ attached to a laptop PC 100 being supplied with power from an AC power source. An AC adapter 123 is connected to the AC power source through an AC cord 125, converts an AC voltage to a predetermined direct current (DC) voltage, and supplies power to the laptop PC 100 through a DC cable 127. Power supplied to the laptop PC 100 is used by a system load of the laptop PC 100 and also used for charging the battery pack 10′. FIG. 7(B) shows the battery pack 10′ attached to and charged by an external battery charger 50′. The same AC adapter 123 that is attached to the laptop PC 100 is connected to the battery charger 50′.
FIG. 8 shows in detail the conventional battery pack 10′ shown in FIG. 7(A) attached to the laptop PC 100. The battery pack 10′ is compliant with the SBS specifications. Provided in the battery pack 10′ are battery cells 11 and electronic components such as a microprocessor unit (MPU) 21, a depletion field effect transistor (D-FET) 17, a complementary field effect transistor (C-FET) 19, a voltage regulator 23, a thermistor 35, a current measurement circuit 13, and a voltage measurement circuit 15. The battery pack 10′ is connected to the laptop PC 100 through five terminals: a positive terminal 37, a C terminal 39, a D terminal 41, a T terminal 43, and a negative terminal 45. Power outputted from the battery cells 11 inside the battery pack 10′ is provided to the laptop PC 100 through the positive terminal 37 and the negative terminal 45. The C terminal 39 and the D terminal 41 are connected to a clock terminal and a data terminal of the MPU 21, respectively, and the T terminal is connected to the thermistor 35.
The MPU 21 is an integrated circuit that operates on a constant voltage provided through the voltage regulator 23. The MPU 21 may include a CPU of 8 to 16 bits or so, a RAM, a ROM, an analog input and output, a timer, and a digital input and output in one package. In addition, the MPU 21 may be capable of executing a program for controlling the battery pack 10′. The MPU 21 uses the current measurement circuit 13 and the voltage measurement circuit 15 to constantly monitor the current and voltage output from the battery 11 and controls the D-FET 17 for discharging of the battery 11 and the C-FET 19 for charging of the battery 11. From the MPU 21, a clock line and a data line lead to the embedded controller 115 of the laptop PC 100 through the C terminal 39 and D terminal 41, respectively, so that the MPU 21 can communicate with the embedded controller 115.
The resistance of the thermistor 35 changes in accordance with temperature. In one embodiment, the thermistor 35 is provided near the battery cells 11 and is connected to a voltage source Vcc through a pull-up resistance 121 of the laptop PC 100, thereby functioning as a temperature measurement circuit. An output from the thermistor 35 is input into the embedded controller 115 through the T terminal 43. The thermistor 35 is used for measuring the temperature of a battery.
The power management function of the laptop PC 100 is implemented by the embedded controller 115 together with a battery charger 117, a control line 119, a DC-DC converter 122, and an AC adapter 123. The embedded controller 115 is an integrated circuit that controls the power supply as well as many hardware components constituting the laptop PC 100. The embedded controller 115 obtains information about the present current value and voltage value of the battery 11 through communication with the MPU 21 and, on the basis of the information, controls the battery charger 117 through the control line 119 to control charging of the battery pack 10′.
Power supplied from the AC adapter 123 and the battery pack 10′ is provided to components in the laptop PC through the DC-DC converter 122. The embedded controller 155 is also connected onto an industry standard architecture (ISA) bus 113, from which the embedded controller 155 is interconnected with and can communicate with a CPU 101, a main memory 105, and other hardware components constituting the laptop PC 100 through connections, including a peripheral component interconnect (PCI) bus 109, a PCI-ISA bridge 111, a CPU bridge 107, and a front side (FS) bus 103. Most of the other hardware components comprising the laptop PC 100 such as a display, a magnetic disk, an optical disk, and a keyboard are well known and therefore not shown in FIG. 8.
FIG. 9 shows in detail the battery pack 10′ shown in FIG. 7(B) attached to an external battery charger 50′. The internal configuration of the battery pack 10′ is the same as that of the battery pack 10′ connected to the laptop PC 100 shown in FIG. 8. The battery charger 50′ includes an MPU 116, a switch (SW) 129, a voltage regulator 51, and a current regulator 53. The MPU 116 plays a roll equivalent to the embedded controller 115 of the laptop PC 100 during charging the battery pack 10′. The MPU 116 obtains charging information such as the present current and voltage of the battery 11 through communication with the MPU 21 and, on the basis of the information, controls the SW 129, the voltage regulator 51, and the current regulator 53 to control charging in a manner similar to that in the laptop PC 100.
The conventional external battery charger 50′ is capable of controlling charging of the battery pack 10′ in a manner similar to that used in the battery charger 117 incorporated in the laptop PC 100. However, such an external battery charger 50′ is costly because it uses an MPU 116. Therefore there is a demand for simplifying the structure of external battery chargers to reduce their costs.